1. Field of the Invention:
The present invention relates to a cancelling device for a turn signal which automatically returns to a neutral position and an operation lever which has been operated to indicate the turning direction of a vehicle when the steering shaft of the vehicle is turned in the direction opposite to that in which the operation lever has been turned.
2. Description of the Related Art:
A conventional cancelling device for a turn signal includes a cam cylindrical body which has two cam portions and which is provided coaxially with respect to the steering shaft, and a turn signal switching mechanism portion operated by means of an operation lever. A ratchet is moved to a cancelling position by the pivoting of the operation lever from a neutral position to a right or left turn position. When the operation lever is pivoted to the right or left turn position and the steering shaft is then turned through a predetermined angle in the same direction as that in which the operation lever is operated, the turning of the steering wheel in the opposite direction causes the cam portions of the cylindrical body pivoted by the steering wheel to abut against the ratchet located at the cancelling position, thereby returning the operation lever to the neutral position. The turn signal switching mechanism portion employed in the above-described cancelling device falls into two types: one type includes a bifurcated bracket with two ratchets respectively used for right and left turns provided at the two end portions thereof, the bracket being provided in such a manner as to surround the cam cylindrical portion and the bracket being pivoted by the operation lever; and the other type includes one ratchet which is provided on the same side of the mechanism portion as that on which the operation lever is provided.
The turn signal switching mechanism portion of the first type has an advantage in that a cancel preparation set separately by changing the limit positions of the two ratchets. The cancel preparation angle is the rotational angle through which the cam position travels as it is moved to a position just past the ratchet which is located at the canceling positioning, when the steering wheel is turned to the right (or to the left) where the operation lever of the turn signal switching mechanism portion has been pivoted from the neutral position to the right (or respectively to the left) turn position and the ratchet has been thereby moved to the canceling position. Subsequent turning of the steering wheel from this position to the left (or respectively to the right) immediately causes the cam portion to abut against the ratchet, thereby causing the operation lever to return to its neutral position. The reverse canceling angle is the rotational angle through which the cam portion travels when it is brought into abutment with the ratchet located at the canceling position to return the operation lever to its neutral position when the steering wheel is turned to the left (or to the right) where the operation lever of the turn signal switching mechanism portion has been pivoted from the neutral position to the right (or respectively to the left) turn position and the ratchet has been thereby moved to the canceling position. The cancel preparation angle in the switching mechanism of the first type is generally set at about 80 degrees and the reverse canceling angle is generally set at 120 degrees or above. However, since the bracket and the ratchets are provided in such a manner that they enclose the cam cylindrical portion, i.e., the steering shaft, the steering wheel must be removed to remove the turn signal switching mechanism portion when the turn signal switching mechanism portion is repaired, making any such repair job a troublesome task.
On the other hand, the turn signal switching mechanism of the second type is advantageous in terms of facilitating the repair thereof, because there is no need for removal of the steering wheel. However, since it has only one ratchet, this precludes the possibility of setting the cancel preparation angle and the reverse cancelling angle at different angles. Thus, if the cancel preparation angle is set at about 80 degrees, the reverse cancelling angle must also be set at approximately 80 degrees. In consequence, when for example the steering wheel is turned to the left in order to pull the vehicle to the left side of a road after the operation lever has been brought to the right turn position, the operation lever returns to its neutral position if the steering wheel is turned through a small angle, which may be about 80 degrees, so the operation lever then has to be brought to the right turn position again.